We can refuse to answer the questions if we want, they're just anonomised statistics for monitoring purposes and the forms generally have a 'refused to answer' box (yep, you've still got to fit into a box I'm afraid!)
I'm not innocent enough to think statistics are really useful but my initial comment still stands that to refer to fellow humans as 'blacks' is offensive and ignorant.
Right, I'm getting off this topic before I get called a wooly liberal!